LaserTweezer – Optical Trap

Summary

Optical Tweezers are scientific instruments to manipulate objects of microscopic size. These can be small plastic beads or biological material like cells. The trapping is achieved by focusing a laser beam on the dielectric particles that are then attracted to the region of strongest electric field, which is the center of the beam. The fact that samples under a microscope can be manipulated gives new possibilities to explore. The force applied on the object depends linearly on its displacement from the trap center just as with a simple spring system. Micro-beads can thus be used as handles and forces can be determined though the interaction. The main component of an optical tweezer are a microscope to see the sample, a laser beam focused on the sample to manipulate, special filter and lenses and a movable stage. The sum of this equipment as used in regular laboratories are usually big and quite expensive. The her after described devices uses only recycled parts from consumer electronics and comes at a fraction of the cost while still reproducing the original concept in a fully functional way. The work is based on the scientific publication “Single-cell isolation using a DVD optical pickup” [1]. The paper describes in detail the setup used and the circuit to power the laser. In fact the DVD head unit comprises some key components such as a powerful laser, a collimator lens as well as a focusing mechanism perfect for the application. However the setup as described in the paper still uses a conventional microscope and specialized filter to prevent the strong laser from shining into the microscope. In the presented setup these elements could further be replaced by using a USB computer web-cam and a filter made from a shutter disc synchronized with an intermittent switching of the small solid state laser. The compact unit of a “DIY Optical Tweezer” now weights less than 500g and can be built entirely from recycled consumer electronic parts at a cost of less than 100$. Sma...